The present invention relates to an engine starter motor and, particularly, to an improvement of a pinion thereof which meshes with a ring gear of an engine.
FIG. 4 shows in cross section a portion of a conventional engine starter motor including an over-running clutch portion thereof. In FIG. 4, reference numeral 1 depicts an electromagnetic switch, 2 a plunger magnetically attracted in an arrow direction by the electromagnetic switch 1, and 3 is a lever rotatable about a point 3a upon an energization of the electromagnetic switch 1 to move the over-running clutch 4 forwardly. 5 depicts an output shaft of the starter motor, 6 is an outer of member the over-running clutch 4 meshing with a helical spline portion 7 of the output shaft 5, and 8 is an inner member of the clutch which has a pinion 9 formed integrally therewith. 10 depicts a bearing provided on an inner surface of the pinion 9 which slides along the output shaft 5, 11 is another bearing provided on a front end of a front bracket 12 for supporting a front end of the output shaft 5, 13 is a stopper provided on the output shaft 5 through a ring 14 for restricting a movement of the pinion 9 along the output shaft 5, 15 is a washer inserted between the front bracket 12 and the output shaft 5, 16 in a yoke of the d.c. motor, and 17 is a field coil for driving an armature 18 of the motor.
In operation, upon an application of a voltage to the electromagnetic switch 1, the plunger 2 is attracted to rotate the lever 3 in a counterclockwise direction about the point 3a to thereby move the over-running clutch 4 forwardly so that the pinion 9 supported thereby meshes with the ring gear of the engine. At the same time, a power supply from a vehicle mounted battery to the d.c. motor through a contact associated with the electromagnetic switch 1 is started, upon which the armature 18 of the d.c. motor is energized and a rotational force thereof is transmitted from the output shaft 5 through the over-running clutch 4 and the pinion 9 to the ring gear of the engine to rotate the latter. The forward movement of the pinion 9 is restricted by the stopper 13.
In the conventional starter motor constructed as above mentioned, the output shaft 5 is subjected to a bending moment due to a reactive force produced in the pinion 9. Particularly, the bending moment may be concentrated to a groove of the ring 14 of the stopper 13. Therefore, the diameter of the output shaft 5 as a whole must be selected large enough to withstand such moment, and a deddendum diameter of the pinion 9 must be large enough accordingly. Thus, the size and number of pinion teeth are restricted, resulting in the design freedom thereof, being degraded. Further, since the pinion 9 and the output shaft 5 are exposed from the front bracket 12, they may be subjected to external dust etc. causing the bearing supporting the pinion 9 to be worn away thereby and making the sliding movement of the pinion 9 difficult.